1. Field of the Invention
The present invention relates to an optical device and a projector.
2. Description of the Related Art
Conventionally, a projector for modulating a light beam irradiated by a light source in accordance with image information to project the light beam in an enlarged manner has been used in a field of presentation and home theater.
A multi-plate projector in which a light beam irradiated by a light source is separated into a plurality of color lights and the respective separated color lights are modulated in order to improve image quality has been known as such projector.
For instance, three-plate projector has an illumination optical system including a light source, a color separating optical system including a dichroic mirror, a plurality of optical modulators, a color combining optical system such as a prism, and a projection optical system.
The illumination optical system has a light source, a light splitting optical device such as an integrator lens, and a light condenser, which splits the light beam irradiated by the light source into a plurality of sub-beams and superposes the respective sub-beams onto an image formation area of the optical modulator.
The color separating optical system has a dichroic mirror that transmits blue light and green light and reflects red light and another dichroic mirror that transits blue light and reflects green light to separate the light beam irradiated by the illumination optical system into red, green and blue lights.
The optical modulator has an optical modulator such as liquid crystal panel, which modulates the incident color light in accordance with image information to form an optical image.
The color combining optical system has a light-incident side to which the optical modulators corresponding to the respective color lights oppose a light-irradiation side for irradiating the combined light beam, which combines the optical image for the respective color lights formed by the respective optical modulators to form a color image.
The projection optical system enlarges and projects the light beam irradiated by the color combining optical system to form a large-screen projection image on a screen.
For instance, when such projectors are used on a desk or a stand, such projector is capable of conducting projection of the optical image where the projection area is shifted slightly upward relative to the optical axis of the projection optical system.
As shown in FIG. 8, the above projection is achieved by shifting optical axis A of a projection optical system 46 in Y(+) direction relative to central axis C of an image formation area of an optical modulator 441 to shift central axis D of a projection area 500 in Y(+) direction relative to the optical axis A of the projection optical system 46.
Conventionally, the central axis C of the image formation area of the optical modulator 441 is aligned with the central axis B of the light-incident side of the color combining optical system 544, and the height of the color combining optical system 544 is set in accordance with the vertical extension of the modulated light beam irradiated by the optical modulator 441.
However, as shown in FIG. 8, according to such conventional arrangement, since the optical axis A of the projection optical system 46 is shifted in Y(+) direction relative to the central axis B of the light-irradiation side of the color combining optical system 544, light beam not taken into the projection optical system 46 is irradiated from the light-irradiation side of the color combining optical system 544 on an end in Y(−) direction.
Accordingly, since the height of the color combining optical system 544 is set so that the light beam not taken into the projection optical system 46 is irradiated from the light-irradiation side, material cost thereof becomes expensive.